How Can Move Semantics Optimize Vector Expansion in C ?

Exploiting Move Semantics for Vector Expansion

When dealing with non-trivial objects in C , it is crucial to leverage move semantics to optimize performance and reduce unnecessary copy operations. This article explores the question of how to enforce move semantics for a vector of objects, ensuring that the move constructor is used when the vector grows.

The problem arises when a vector of objects like std::vector<A> is populated, using functions like push_back(a). By default, the vector uses the copy constructor, instantiating new copies of the elements. To overcome this, the move constructor of class A can be invoked by informing C and the std::vector that the move constructor and destructor are exception-safe, using noexcept.

The noexcept specifier assures the compiler that the move constructor doesn't throw exceptions. By implementing the move constructor with noexcept, as seen in the code below, the move constructor will be invoked when the vector expands:

A(A && rhs) noexcept { 
  std::cout << "i am the move constr" <<std::endl;
  ... some code doing the move ...  
  m_value=std::move(rhs.m_value) ; // etc...
}

This approach aligns with the C standard, which necessitates strict exception guarantees for operations performed by std::vector.

For optimal efficiency, consider using the emplace_back method instead of push_back, as it avoids unnecessary copying. It is worth noting that early versions of Visual Studio 2015 and older may not support this feature, despite supporting move semantics.

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